1. Field of the Invention
The present invention relates to a photoelectric converting device and, more particularly, to a photoelectric converting device for use in an input section of an image processing apparatus, such as a facsimile apparatus, an image reader, a copier, an electronic blackboard, or the like.
2. Related Background Art
In recent years, a long line sensor having an equal magnification optical system has been developed as a photoelectric converting device in order to realize a miniaturization and a high performance of the facsimile apparatus, image reader, and the like.
Hitherto, such a kind of line sensor is constructed by connecting an integrated circuit (hereinafter, abbreviated to IC) for signal processing in which switching elements and the like are respectively constructed for photoelectric conversion elements arranged like an array of one line. However, as the number of photoelectric conversion elements, 1728 elements are needed in the case of the A4 size according to the G3 standard of the facsimile apparatus. Therefore, the number of installing steps also increases and a line sensor which sufficiently satisfies requirements regarding the manufacturing costs and the reliability is not obtained yet.
On the other hand, hitherto, a construction by matrix wirings has been used as a construction to reduce the number of signal processing ICs and to reduce the number of installing steps.
There has also been tried to cheaply provide an image reading apparatus of the long contact type in which thin film transistors (hereinafter, abbreviated to TFT) are used as switching elements and an integrated structure comprising photoelectric conversion elements, thin film transistors, matrix wirings, and the like is used, thereby reducing the function of a signal processing IC and realizing a high reading speed.
Further, to provide an image reading apparatus of the long contact type of low manufacturing costs and a high reliability, there has also been developed a method whereby the photoconductive converting layer of the photoelectric conversion element and the semiconductor layer of the TFT are formed by the same material such as amorphous silicon and the photoelectric conversion elements, TFT, matrix wirings, and the like are integratedly formed on the same substrate by using the same manufacturing steps.
Further, to realize miniaturization and low costs, there has also been proposed a photoelectric converting device in which the photoelectric conversion element directly detects the reflected light from an original through a transparent spacer such as a glass or the like without using an equal magnification fiber lens array.
FIG. 1 shows an equivalent circuit diagram of a conventional photoelectric converting device which has already been proposed.
Light information which enters photoelectric conversion elements S.sub.1-1 to S.sub.36-48 is transmitted from the photoelectric conversion elements S.sub.1-1 to S.sub.36-48 through accumulation capacitors C.sub.s1-1 to C.sub.s36-48, transfer TFTs T.sub.1-1 to T.sub.36-48, resetting TFTs R.sub.1-1 to R.sub.36-48, and matrix signal wirings L.sub.1 to L.sub.48 and become parallel voltage outputs. Further, the parallel voltage outputs are supplied to a read switch IC and become a serial signal. The serial signal is taken out to the outside.
In an example of a construction of the above conventional photoelectric converting device, the photoelectric conversion elements of 1728 bits corresponding to the total number of pixels are divided into 36 blocks every 48 bits. The operations of the 36 blocks are sequentially executed on a block unit basis. FIG. 2 shows a timing chart when an original of a uniform image concentration is read by the conventional photoelectric converting device.
The light information which enters the photoelectric conversion elements S.sub.1-1 to S.sub.1-48 of the first block is converted into photo currents and are accumulated as charges into the accumulation capacitors C.sub.s1-1 to C.sub.s1-48. After the elapse of a predetermined time, a first voltage pulse to transfer is applied to a gate drive line G.sub.1 for a time t.sub.1, thereby switching the transfer TFTs T.sub.1-1 to T.sub.1-48 to the on state. The charges in the accumulation capacitors C.sub.s1-1 to C.sub.s1-48 are transmitted through the matrix signal wirings L.sub.1 to L.sub.48 and are transferred to load capacitors C.sub.L1 to C.sub.L48, so that potentials V.sub.L1 to V.sub.L48 of the load capacitors rise (transfer operation).
Subsequently, a voltage pulse is sequentially supplied from a shift register SR.sub.2 to gate drive lines g.sub.1 to g.sub.48 and read switches T.sub.sw1 to T.sub.sw48 are sequentially switched to the on state, thereby converting the signals of the first block which were transferred to the load capacitors C.sub.L1 to C.sub.L48 into the serial signal. After completion of the impedance conversion, the serial signal is read out to the outside of the photoelectric converting apparatus.
After that, a voltage pulse C.sub.res to reset is supplied to reset switches R.sub.sw1 to R.sub.sw48 for a time t.sub.2, thereby resetting the load capacitors C.sub.L1 to C.sub.L48.
Then, a voltage pulse is suppled to a gate drive line G.sub.2 and the transfer operation of the second block is started. At the same time, the reset TFTs R.sub.1-1 to R.sub.1-48 are turned on, the charges in the accumulation capacitors C.sub.s1-1 to C.sub.s1-48 of the first block are reset, thereby preparing for the next readout operation.
In a manner similar to the above, by sequentially driving gate drive lines G.sub.3, G.sub.4, . . . , the data of one line is generated.
In the conventional photoelectric converting device, the transfer operation, reading operation, and resetting operation are sequentially executed on a block unit basis as mentioned above. Therefore, the image signal from the photoelectric converting apparatus is intermittently generated as shown by V.sub.out in FIG. 2.
To use the conventional photoelectric converting device as an image input section of a system such as a facsimile apparatus or the like, there is a case where a problem such that a processing circuit to convert the intermittent signals which are generated from the photoelectric converting apparatus into the continuous signal is needed and a correction circuit to execute a shading correction and the like becomes complicated occurs.
For instance, processes for temporarily storing the signal output of the photoelectric converting device into a line memory before it is image processed and, thereafter, for converting the intermittent signals into the continuous signal are necessary. Or, it is necessary to non-continuously execute the image process.
Consequently, in the conventional photoelectric converting device, there is a case where problems such that the costs of the whole system rise and the like occur.